If you un-upvote you don't get the vote power back. So you just lose that vote. It surprised me when someone told me that so I tested it to confirm it.
Also, how are you working out which position you are in? The drop down list doesn't reflect timing as far as I know. There's no way for someone to bump you in the timing of votes. It could be they're voting while you're reading the article and you haven't refreshed the page when you vote?
RE: Steemit: Curation League Week 8 - New users, and a new Leader!